Nutritional mineral fortification of milk

ABSTRACT

A calcium and/or nutritional mineral fortified milk or milk powder product utilises pyrophosphates or orthophosphates in combination with maintenance of pH within the range of 6.5 to 7.5 to render the milk heat stable. Additional calcium and/or nutritional mineral is added in soluble form either before or after the phosphate addition. The preferred orthophosphates are one or more of monosodium dihydrogen orthophosphate, disodium hydrogen orthophosphate, trisodium orthophosphate, monopotassium dihydrogen orthophosphate, dipotassium hydrogen orthophosphate and tri potassium orthophosphate. Addition of an alkaline agent to adjust the pH is not needed if an appropriate mix of orthophosphates is used. The milk products or milk products recombined from milk powders are heat stable and do not have the problems of translucency, gritty mouth feel or sedimentation which can be associated with other stabilised fortified milks.

TECHNICAL FIELD

[0001] The present invention relates to a process for producing calciumor other nutritional mineral fortified milk, toned milk, or milkpowders.

BACKGROUND TO THE INVENTION

[0002] Calcium is a mineral essential in human nutrition and comprisesapproximately 1.5 to 2 percent of total adult body weight. Besidesproviding the skeletal structure for bones and teeth, calcium plays akey role in many other day-to-day functions of the body. Calcium isimportant for the normal clotting of blood, the conduction of nerveimpulses, the contraction and relaxation of muscles as well as theregulation of body fluids, hormone secretion and cell division.

[0003] Calcium has received increased attention in dietary regimes inrecent times because of its possible role in the prevention of diseasessuch as osteoporosis. The recommended daily allowance (RDA) for calciumis 1200 mg for women and 800 mg for men. Dairy products are consideredan excellent source of calcium and the RDA is essentially met throughthe intake of dairy products.

[0004] Milk is a dairy product and as such a source of calcium. Milkgenerally contains 1200 mg per litre of calcium. However, as the demandfor calcium has increased, it has become necessary to produce calciumfortified milk with a larger amount of calcium in a single serve.

[0005] A calcium fortified milk provides to people who do not choose toconsume large amounts of dairy products an alternative to calciummineral supplements.

[0006] Some Calcium fortified milk products use relatively insolubleforms of calcium such as tricalcium phosphate or calcium carbonate thathave the disadvantage of having a gritty taste and sedimentation of thecalcium salt. These forms of calcium require the use of suspensionagents to maintain the calcium in suspension.

[0007] It has been observed that the addition of calcium salts to milkcauses a drop in pH. This drop in pH is thought to be one reason forlack of heat stability in such calcium fortified milks wheresedimentation occurs after pasteurisation. The raised calcium activityof milks with added calcium also contributes to heat instability. Thishas led some producers to add calcium after pasteurisation.

[0008] The specification of U.S. Pat. No. 5,449,523 discloses a processfor the preparation of a calcium fortified yoghurt. The process includesthe steps of mixing a fermentable dairy product with an alkaline agent,a chelating agent [preferably alkali metal citrates] and a source ofsoluble calcium. The alkaline agent and chelating agent are added to themixture in amounts effective to maintain the pH of the yoghurt base mixabove about 6.7. The yoghurt base mix is then pasteurised, cooled andinoculated with a yoghurt starter. The specification states that theinvention is based on the unexpected discovery that the heat stabilityof yoghurt can be dramatically improved if the pH is not allowed to dropbelow about 6.7 prior to pasteurisation. Furthermore, a source ofadditional calcium can be added to the milk whilst maintaining the pHabove 6.7 by adding a chelating agent and/or an alkaline agent atapproximately the same time as the source of calcium in amountseffective to prevent the pH from dropping below 6.7. Experience hasshown that milk stabilised with citrates and other chelating agentssuffer from translucency apparently caused by migration of calcium fromthe protein micelles and release of casein into the serum.

[0009] Increasingly other nutritional minerals such as magnesium iron,zinc are being added to milk and milk products.

[0010] It is an object of this invention to provide heal: stable calciumand other nutritional mineral fortified milks that do not suffer any ofthe defects discussed above.

[0011] A further object of this invention is to produce calcium andother nutritional mineral fortified milk powders that have good heatstability when reprocessed after reconstitution.

BRIEF DESCRIPTIONS OF THE INVENTION

[0012] This invention is predicated on the discovery that calcium and/ornutritional mineral fortified milk can be stabilised by the addition ofan effective amount of a phosphate which enables calcium and/ornutritional minerals to migrate into the protein micelles and maintainsthe pH so that it lies within a range from 6.5 to 7.5 preferably betweenpH 6.8-7.0. This is in contrast to the effect of chelating agents suchas citrates and polyphosphates which at high concentrations disintegratethe casein micelle causing migration of calcium from the micelles andreleasing casein into the serum. In contrast the phosphate addedaccording to the present invention preserves the integrity of the caseinmicelles.

[0013] Throughout this specification the term milk or fortified milkmeans a milk based product including fresh milk, reconstituted milk,modified milk or enriched milk that is either intended as a beverage oras an ingredient to be used for further processing. The ingredient maybe milk, concentrated milk or milk powder and further processingincludes processing to make other dairy products such as cheese,yoghurt, powdered milk starting from milk, concentrated milk or milkpowder.

[0014] Nutritional minerals other than calcium are iron, magnesium, zincor manganese.

[0015] Accordingly, the present invention provides a process forproducing a calcium or nutritional mineral fortified milk, the processincluding the steps of:

[0016] adding a soluble calcium and/or a nutritional mineral compound toa milk,

[0017] adding either before or after the calcium and/or nutritionalmineral addition an effective amount of a phosphate which enables thecalcium and/or nutritional mineral to migrate into the protein micellesand maintains the pH so that it lies within a range from 6.5 to 7.5

[0018] The preferred phosphate is a pyrophosphate or orthophosphate andis preferably one or more of monosodium dihydrogen orthophosphate,disodium hydrogen orthophosphate, tri sodium orthophosphate,monopotassium dihydrogen orthophosphate, dipotassium hydrogenorthophosphate and tri potassium orthophosphate

[0019] In a further aspect, the present invention provides a calcium ornutritional mineral fortified milk which includes milk, a solublecalcium or nutritional compound and an amount of a phosphate whichenables calcium or the nutritional mineral to migrate into the proteinmicelles and maintains the pH so that it lies within a range from 6.5 to7.5, effective in stabilising the milk during heat treatment.

[0020] The added calcium or nutritional mineral according to the presentinvention does not require the addition of suspension agents. Preferablythe calcium and/or nutritional mineral is added as a soluble salt. It isthought that the minerals added to the milk migrates, in the presence ofortho phosphate, into the micelle phase of the milk where it is held incolloidal suspension in the micelles. Other forms of soluble calcium ornutritional mineral when added with chelating agents such as citrateshave the opposite effect of encouraging calcium migration out of themicelles which results in the translucent appearance of the milk.Because the orthophosphates encourage migration into the micelles theupper limit to calcium fortified content in heat stable milks is alsoincreased.

[0021] The pH range which ensures heat stable fortified milk is widerwhen using the phosphates of this invention than is the case withchelating agents such as citrates. The pH of the calcium fortified milkmay be controlled by the addition of an appropriate phosphate ororthophosphate or mix of phosphates or orthophosphates. For example,trisodium orthophosphate is highly alkaline, disodium orthophosphate isslightly alkaline and monosodium orthophosphate is mildly acidic. It isalso within the scope of this invention to adjust the pH within therange of 6.5 to 7.5 using an appropriate food grade alkali or acid. Thequantity of alkaline agent added to the calcium fortified milk issufficient to cause the pH to fall within the specified range. Optimallythis is close to pH 7, but adequate heat stability can be achieved ifthe pH lies in a range between 6.5 and 7.5.

[0022] The amount of orthophosphate added to the calcium fortified milkis largely dependent upon the amount of additional calcium added to themilk and the heat treatment to be applied. Normally, sufficientorthophosphate is added to the milk so that the ratio of added calciumto added orthophosphate is 1:1 on a molar basis. Higher or lower ratiosmay be utilised depending on the inherent heat stability of the milk andthe level of calcium fortification. However, the ratio of added calciumto added orthophosphate would normally lie in a range from 2:1 to 1:2 ona molar basis when a high heat treatment (for example 90° C. for 10minutes) is required. Lower levels of phosphate may be suitable toprovide adequate heat stability under pasteurisation conditions (eg 72°C. for 30 seconds).

[0023] In a preferred form of the invention, 8 g of calcium is added perkilogram of finished calcium enriched skim milk solids. Thus, the actuallevel of calcium addition is dependent on the level of milk solids inthe milk to be fortified. According to the standard text: P. Walstra andR. Jenness, “Dairy Chemistry and Physics”, John Wiley & Sons, New York(1984), the calcium content of skimmed milk (containing 9 to 9.50,%solids) is in the range 1200 to 1300 mg/litre. Therefore, if forexample, a kilogram of standard skimmed milk contains 92.5 g of solidsand 1250 mg/litre of calcium, then the required level of calciumaddition would be 785 mg of calcium per kilogram of milk. The preferredlevel addition for the other nutritional minerals is intended to deliverthe maximum recommended daily allowance per 100 g of fortified milksolids. For iron zinc and manganese these are very small amountscompared to the daily requirements for calcium and magnesium.

[0024] In some cases when the correct form of orthophosphate is used,the alkaline agent may not be required depending on the condition of themilk and the season of the year. When other forms of orthophosphate areused, the quantity of alkaline agent required will be higher, but againit will also depend on inherent milk properties.

[0025] The order of addition of calcium compound orthophosphate and pHadjustment agent to the milk is not critical. Although it is obviouslyeasier to correctly adjust the pH, if needed, after the calcium compoundand the orthophosphate have been added.

[0026] The calcium and/or nutritional mineral fortified milk of thepresent invention can be pasteurised (eg 72° C. for 30 seconds) or heattreated at a range of other conditions (eg: 90° C. for 10 minutes). Thelow or high heat treatment of milk prior to concentration and drying toproduce milk powder imparts specific attributes to milk powders. Forexample, a high heat treatment improves the water binding capacity,viscosity and gelation characteristics of the milk when reconstitutedand used in specific applications. Low heat treatment and high heattreatment will produce milk powders that conform to either a low or highheat specification based on the whey protein nitrogen index (WPNI), thespecification used in the international trade for skimmed milk powders.A multitude of other heating conditions is in use in the industry, whichwill achieve the same WPNI specifications.

[0027] The milk may be homogenised before or after addition of thecalcium source.

[0028] The addition of an appropriate mix of pyrophosphates ororthophosphates to the milk or toned milk maintains the pH range similarto that of conventional milk. A resultant improvement in heat stabilityallows one to prepare a calcium-fortified milk wherein the calciumsource can be added to the milk prior to heat treatment and/orpasteurisation without the undesirable formation of a milk proteinprecipitate.

[0029] The milk or toned milk may be homogenised. Any commonly employedhomogenisation conditions can be satisfactorily employed in the presentinvention.

[0030] The heating step is carried out using techniques well known inthe field, preferably at specified times and temperatures. At highlevels of calcium fortification ultra-high temperatures are generallynot employed for heating.

[0031] The milk or toned milk thus obtained can be enriched with calciumto a level 60% above that of the untreated milk.

[0032] In a third aspect of the invention, there is provided a processfor producing a calcium fortified milk or toned milk powder, the processincluding the steps of:

[0033] adding a soluble calcium and or/a nutritional mineral compound toa milk,

[0034] adding either before or after the calcium and/or nutritionalmineral addition an effective amount of a phosphate which enablescalcium and/or nutritional mineral to migrate into the protein micellesand maintains the pH so that it lies within a range from 6.5 to 7.5

[0035] pasteurising or heating the calcium fortified milk, and

[0036] concentrating and dehydrating the milk to form a calcium and/ornutritional mineral fortified dry milk or toned milk powder.

[0037] The calcium compound employed in the present invention is anyfood grade calcium source preferably a water-soluble calcium salt suchas calcium gluconate, calcium chloride and calcium hydroxide. Thenutritional mineral salts are also food grade water soluble chlorides orsalts usually used in foods The orthophosphate preferably employed inthe present invention includes monosodium dihydrogen orthophosphate,disodium hydrogen orthophosphate, trisodium orthophosphate,monopotassium dihydrogen orthophosphate, dipotassium hydrogenorthophosphate and tri potassium orthophosphate.

[0038] It is preferred that the sequence of addition of theabove-mentioned substances to the milk is orthophcosphate, followed bycalcium and/or nutritional mineral source and alkaline or acidifyingagent if necessary.

[0039] The alkaline agent utilised in the process is preferably any foodgrade alkaline agent that has a minimal effect on the taste, or smell ofthe milk or toned milk. Preferred alkaline agents include alkali metalhydroxides. Preferred alkali metal hydroxides include potassiumhydroxide, sodium hydroxide or mixtures thereof.

[0040] A resultant improvement in heat stability allows one to prepare acalcium-fortified milk wherein the calcium source can be added to themilk prior to heat treatment and/or pasteurisation without theundesirable formation of a milk protein precipitate.

[0041] The dehydration step can be carried out using a variety ofconventional techniques including spray drying, roller drying and freezedrying, however, spray drying is a preferred means for dehydration.Spray drying of the calcium fortified and concentrated milk or tonedmilk can be conducted under conventional conditions.

[0042] The milk or toned milk powder thus obtained is enriched withcalcium some 60% above that of the untreated milk or toned milk.

[0043] In another aspect of this invention there is provided a method oftesting to determine the heat sensitivity of the milk and consequentlythe type and quantity of phosphate needed to stabilise the fortifiedmilk.

[0044] The first method is simply to add a predetermined amount ofcalcium salt and orthophosphate and measure the pH. If the pH is withinthe range of 6.5 to 7.5 no further action is needed. If the pH liesoutside that range the pH may be adjusted or the mix of ortho phosphateschanged to bring the pH within the desired range of 6.5 to 7.5.

DETAILED DESCRIPTION OF THE INVENTION

[0045] In order to demonstrate the present invention, a number ofexperiments were conducted by the present inventors. The experimentsinvestigated a process of producing calcium fortified milk or toned milkand further to this the production of calcium fortified milk and tonedmilk dry powder.

EXAMPLE1

[0046] The use of a range of phosphates (orthophosphate, pyrophosphate,tripolyphosphate, polyphosphate) for stabilising Ca fortified milks wasexamined. Each of these has a differing effect on milk and could be usedto stabilise Ca fortified milks (See Table 1). Without additives, skimmilks (10% milk solids) with 20 mM added calcium form a precipitate onheating at 90° C. for 10 min. The effect of added citrate and longerchain phosphates ( polyphosphate), which is commonly used to stabiliseCa fortified milks, are included for comparison.

[0047] It was observed that citrate and the polyphosphate have atendency to cause the milk to lose its whiteness (before heating) and itmay take on a undesirable greenish—yellowish hue. TABLE 1 Use ofdifferent additives for stabilising reconstituted skim milks (10% skimmilk solids) with added ˜20 mM added Ca under selected conditions.Before heat After heat (90° C./10 min) Free Ca activity Viscosity TotalCa Supernatant Ca Additive pH (mM) (cPoise) (mg/litre) (mg/litre)Control skim milk (10% milk solids) without added Ca at the natural pHNone* 6.63 1.78 1.7 1470 1450 Skim milk (10% milk solids) with added Caat pH ˜7 20 mM orthophosphate* 6.91 1.29 2.3 2290 2280 (K₃PO₄/K₂HPO₄mix)* 4 mM pyrophosphate 7.12 2.5 2.3 nd nd (Na₄P₂O₇) 4 mMtripolyphosphate 7.00 2.54 2.4 2270 2220 (Na₃P₃O₁₀) 8 mMtripolyphosphate 7.00 1.1 2.7 2240 2220 (Na₃P₃O₁₀) 12 mMtripolyphosphate 7.01 0.64 3.2 2260 2260 (Na₃P₃O₁₀) 0.15% Polyphosphate7.01 2.45 2.4 2580 2470 (Calgon T) 10 mM Na₃citrate 7.00 2.65 2.0 22502230 20 mM Na₃citrate 7.00 1.86 2.0 2090 2120

[0048] Supernatant Ca is that remaining in the supernatant of heatedmilk after low speed centrifugation (182 g for 10 min). It is anindication of calcium that is not precipitated by the heating process;n=data not recorded, na—not applicable

EXAMPLE 2

[0049] Table 2 shows the effects of added orthophosphates on heatstability of Ca fortified milks with 20 mM added calcium. When noorthophosphate is added, skim milks (10% milk solids) with 20 mM addedcalcium form a precipitate on heating at 90° C. for 10 min. Milks with a1 to 1 molar ratio of added Ca to added phosphate are stable from ˜ppH6.4 to pH 7.8. By altering the ratios of added tri-:di-:mono-potassiumorthophosphate the pH may be adjusted within the range 7.1 to 5.8without the use of added NaOH. TABLE 2 Heat stability- pH profile for Cafortified skim milks (10% milk solids containing 20 mM added calcium)stabilised with added orthophosphates Before heat Type of addedphosphate Free After heat (90° C./10 min) Added Added Added CalciumViscosity¹ Sediment² K₃PO₄ K₂H PO₄ KH₂ PO₄ pH (mM) (cPoise) (ml/50 mlmilk) — — — 6.19 13.1 precipitated nd 20 mM — — 7.67 0.55 2.8 0.1 20 mM— — 7.61 0.77 3.2 0.3 20 mM — — 7.56 0.64 2.6 0.2 20 mM — — 7.43 0.762.6 0.1 20 mM — — 7.33 0.88 2.5 0.2 20 mM — — 7.23 0.95 2.6 0.1 20 mM —— 7.19 1.02 2.7 0.1 20 mM — — 7.04 1.38 2.5 <0.1 16 mM    4 mM — 6.891.62 2.3 0.1 12 mM    8 mM — 6.75 1.98 2.4 0.2  8 mM    12 mM — 6.632.22 2.5 <0.1  4 mM    16 mM — 6.52 2.72 2.5 0.2 —    20 mM — 6.41 3.364.2 0.1 —    16 mM    4 mM 6.28 4.16 7.0 0.5 —    12 mM    8 mM 6.145.33 precipitated nd —    8 mM    12 mM 6.01 6.71 precipitated nd —    4mM    16 mM 5.86 9.49 precipitated nd — —    20 mM 5.79 9.42precipitated nd

EXAMPLE 3

[0050] Table 3 shows the effects of added tripolyphosphate on heatstability of Ca fortified milks with 20 mM added Ca. These examplesdemonstrate that tripolyphosphate is effective in stabilising Cafortified milks over a wide range of pH when the correct ratio of addedCa added tripolyphosphate is used. Visual examination of the milks withadded tripolyphosphate indicated that these milks developed anundesirable translucency TABLE 3 Heat stability - pH profile for Cafortified skim milks (10% milk solids containing 20 mM added calcium)containing tripolyphosphate at three concentrations Before Added heatAfter heat Sodium Free (90° C./10 min) Tripolyphosphate CalciumViscosity¹ Sediment² (Na₃P₃O₁₀) pH (mM) (cPoise) (mg/50 ml) 0 6.19 13.61      precipitated   nd 4 mM 6.14  6.38    >20  nd 4 mM 6.39* 4.967.4 14  4 mM 6.65* 3.64 2.6 0.7 4 mM 6.69* 3.23 2.5 1  4 mM 6.84* 2.932.6 0.2 4 mM 7.02* 2.41 2.3 0.1 4 mM 7.22* 1.89 2.5 0.2 4 mM 7.51* 1.502.7 0.2 8 mM 6.29  2.47 2.6 0.9 8 mM 6.56* 1.76 2.6 0.5 8 mM 6.69* 1.532.7 0.2 8 mM 6.84* 1.28 2.8 0.2 8 mM 7.08* 0.93 2.7 0.1 8 mM 7.17* 0.852.8 0.2 8 mM 7.36* 0.71 2.9 0.1 8 mM 7.82* 0.48 4.7 0.4 12 mM  6.51 1.27 2.4 0.1 12 mM  6.75* 1 2.6 0.2 12 mM  6.88* 0.8 2.8 0.1 12 mM 7.03* 0.71 3.8 0.2 12 mM  7.14* 0.62 14.4  0.3 12 mM  7.34* 0.53    >200.2 12 mM  7.54* 0.44    >20  nd 12 mM  7.79* 0.34    >20  nd

EXAMPLE 4

[0051] 15 Table 4 shows the effects of added pyrophosphate on heatstability of Ca fortified milks with 20 mM added Ca. Pyrophosphates areless effective in providing heat stability and they also cause anincrease in the viscosity of the calcium fortified milks, both beforeand after heating. At lower pH values, gels form in Ca fortified milkswith added pyrophosphate before heating. Other studies have previouslyshown that pyrophosphates increase the viscosity of milk. Vujicic I.,deMan J. M., and Woodrow I. L. “Interaction of Polyphosphates andCitrates with Skim milk Proteins.”, Can. Inst. Food Technol. J. 117(1968) TABLE 4 Heat stability- pH profile for Ca fortified skim milks(10% milk solids containing 20 mM added calcium) containingpyrophosphate at two concentrations Added Before heat Sodium Free Afterheat (90° C./10 min) milk solids Pyrophosphate Calcium ViscosityViscosity¹ Sediment² non-fat (Na₄P₂O₇) pH (mM) (cPoise) (cPoise) (mL/50ml) 10% 0   6.19 13.61 nd precipitated nd 10% 4 mM 6.19 7.37 nd nd nd10% 4 mM 6.44 5.31 nd <20 nd 10% 4 mM 6.57 4.57 nd 2.8 1.6 10% 4 mM 6.684.03 nd 2.3 1.2 10% 4 mM 6.81 3.24 nd 2.2 0.6 10% 4 mM 6.94 3.35 2.182.5 0.6 10% 4 mM 7.12 2.5 nd 2.3 0.5 10% 4 mM 7.28 2.17 nd 2.3 0.1 10% 4mM 7.56 1.66 nd 2.4 0.4 10% 8 mM 6.30 nd gel nd nd 10% 8 mM  6.53* ndgel nd 5.0 10% 8 mM  6.75* nd gel nd 3.5 10% 8 mM  6.85* nd 5.7 8.3 5.010% 8 mM  7.02* nd 4.9 4.5 1.3 10% 8 mM  7.21* nd 4.1 4.5 1.0 10% 8 mM 7.49* nd 3.7 4.0 0.1 10% 8 mM  8.09* nd 3.2 3.8 0.3

[0052] The method for production of selected Ca fortified powders aregiven in Examples 5-10 below. The characteristics of the powders and theheat stability of milks reconstituted from these powders are given inTable 5.

EXAMPLE 5 Production of Low Heat Skim Milk Powder ContainingApproximately 8 g Added Calcium Per kg Final Powder (1:1 Molar Ratio ofCalcium Chloride to Tripotassium Orthophosphate)

[0053] Solutions of calcium chloride (9.515 kg of 0.2 mole/kg CaCl₂solution) and tripotassium orthophosphate (9.515 kg of 0.2 mole/kg K₃PO₄solution) were mixed with skim milk (100 kg milk containing 8.9% milksolids non-fat). To this mixture was added 0.644 kg hydrochloric acidsolution (1 mole/kg). The pH of the final mixture was 7.1. The Cafortified milk mixture was pasteurised at 72° C. for 30 sec,concentrated to ˜45% total solids using a double effect falling filmevaporator and dried to ˜4% moisture in a Niro Production Minor.

EXAMPLE 6

[0054] Production of High Heat Skim Milk Powder Containing Approximately8 g Added Calcium Per kg Final Powder (1:1 Molar Ratio of CalciumChloride to Tripotassium Orthophosphate)

[0055] Solutions of calcium chloride (9.515 kg of 0.2 mole/kg CaCl₂solution) and tripotassium orthophosphate (9.515 kg of 0.2 mole/kg K₃PO₄solution) were mixed with skim milk (100 kg milk containing 8.9% milksolids non-fat). To this mixture was added 0.644 kg hydrochloric acidsolution (1 mole/kg). The pH of the final mixture was 7.1. The Cafortified milk mixture was heated at 90° C. for 10 min, concentrated to45% total solids using a double effect falling film evaporator and driedto 4% moisture in a Niro Production Minor.

EXAMPLE 7 Production of Low Heat Skim Milk Powder ContainingApproximately 8 g Added Calcium Per kg Final Powder (1:1 Molar Ratio ofCalcium Chloride to Monosodium Dihydrogen Orthophosphate)

[0056] Solutions of calcium chloride (9.510 kg of 0.2 mole/kg CaCl₂solution) and tripotassium orthophosphate (9.510 kg of a solutioncontaining 0.2 mole NaH₂PO₄ and 0.32 mole KOH/kg) were mixed with skimmilk (100 kg milk containing 8.9% milk solids non-fat). To this mixturewas added 0.6 kg potassium hydroxide solution (1.0 mole/kg). The pH ofthe final mixture was 7.0. The Ca fortified milk mixture was pastuerisedat 72° C. for 30 sec, concentrated to ˜45% total solids using a doubleeffect falling film evaporator and dried to ˜4% moisture in a NiroProduction Minor.

EXAMPLE 8 Production of High Heat Skim Milk Powder ContainingApproximately 8 g Added Calcium Per kg Final Powder (1:1 Molar Ratio ofCalcium Chloride to Monosodium Dihydrogen Orthophosphate)

[0057] Solutions of calcium chloride (9.510 kg of 0.2 mole/kg CaCl₂solution) and tripotassium orthophosphate (9.510 kg of a solutioncontaining 0.2 mole NaH₂PO₄ and 0.32 mole KOH/kg) were mixed with skimmilk (100 kg milk containing 8.9% milk solids non-fat). To this mixturewas added 0.6 kg potassium hydroxide solution (1.0 mole/kg). The pH ofthe final mixture was 7.0. The Ca fortified milk mixture was heated at90° C. for 10 min, concentrated to ˜45% total solids using a doubleeffect falling film evaporator and dried to ˜4% moisture in a NiroProduction Minor.

EXAMPLE 9 Production of Low Heat Full-Cream Milk Powder ContainingApproximately 8 g Added Calcium Per kg Final Powder (1:1 Molar Ratio ofCalcium Chloride to Monosodium Dihydrogen Orthophosphate)

[0058] Solutions of calcium chloride (13.89 kg of 0.2 mole/kg CaCl₂solution) and monosodium dihydrogen orthophosphate (13.89 kg of asolution containing 0.2 mole NaH₂PO₄ and 0.32 mol KOH/kg) were mixedwith full-cream milk (100 kg milk containing 8.9% milk solids non-fatand 4% fat). The pH of the final mixture was 6.9. The Ca fortified milkmixture was pasteurised at 72° C. for 30 sec, concentrated to ˜45% totalsolids using a double effect falling film evaporator and dried to ˜4%moisture in a Niro Production Minor.

EXAMPLE 10 Production of High Heat Full-Cream Milk Powder ContainingApproximately 8 g Added Calcium Per kg Final Powder (1:1 Molar Ratio ofCalcium Chloride to Monosodium Dihydrogen Orthophosphate)

[0059] Solutions of calcium chloride (13.89 kg of 0.2 mole/kg CaCl₂solution) and monosodium dihydrogen orthophosphate (13.89 of a solutioncontaining 0.2 mole NaH₂PO₄ and 0.32 mol KOH/kg) were mixed withfull-cream milk (100 kg milk containing 8.9% milk solids non-fat and 4%fat). The pH of the final mixture was 6.9. The Ca fortified milk mixturewas heated at 90° C. for 10 min, concentrated to ˜45% total solids usinga double effect falling film evaporator and dried to ˜4% moisture in aNiro Production Minor. TABLE 5 Characteristics of milks obtained onreconstitution of Ca fortified powders at (skim milks: 10%, full creammilks 12.5% total solids,) Reconstituted Milks Viscosity Viscosity afterheating before (90° C./ Total Ca heating 10 min) Examples pH mg/litre(cPoise) (cPoise) Low heat skim milk 7.0 2170 2.2 2.1 powder containingapproximately 8 g added calcium per kg final powder (1:1 molar ratio ofcalcium chloride to tripotassium orthophosphate) High heat skim milk 7.02125 2.3 2.1 powder containing approximately 8 g added calcium per kgfinal powder (1:1 molar ratio of calcium chloride to tripotassiumorthophosphate) Low heat skim milk 6.8 2110 2.2 2.0 powder containingapproximately 8 g added calcium per kg final powder (1:1 molar ratio ofcalcium chloride to monosodium dihydrogen orthophosphate) High heat skimmilk 6.8 2095 2.4 2.0 powder containing approximately 8 g added calciumper kg final powder (1:1 molar ratio of calcium chloride to monosodiumdihydrogen orthophosphate) Low heat full-cream milk 6.6 2210 3.5 4.4powder containing approximately 8 g added calcium per kg final powder(1:1 molar ratio of calcium chloride to monosodium dihydrogenorthophosphate) High heat full-cream milk 6.5 2205 3.5 2.5 powdercontaining approximately 8 g added calcium per kg final powder (1:1molar ratio of calcium chloride to monosodium dihydrogen orthophosphate)powder

EXAMPLE 11

[0060] The addition of magnesium to milk is illustrated in table 6. 20mM magnesium was added with orthophosphates. When no orthophosphate isadded, skim milks (10% milk solids) with 20 mM added magnesium form aprecipitate on heating at 90° C. for 10 min. The non fat milk solids inall of the compositions was 10%. TABLE 6 Heat stability- pH profile forCa fortified skim milks (10% milk solids containing 20 mM addedmagnesium) stabilised with added orthophosphates Before After heat heat(90° C./10 min) Added Added Added Free Vis- Sedi- K₃PO₄ K₂H PO₄ KH₂ PO₄pH Calcium cosity¹ ment² 0 0 0 6.37 4.31 precip- nd itated 20 mM  8.42*0.09 3.6 <0.1 20 mM  8.14* 0.14 3.9 0.1 20 mM  8.00* 0.18 3.2 <0.1 20 mM 7.89* 0.20 2.8 0.1 20 mM  7.77* 0.24 2.4 <0.1 20 mM  7.71* 0.24 2.3<0.1 20 mM 7.56 0.3 2.7 <0.1 16 mM 4 mM 7.29 0.36 2.1 0.1 12 mM 8 mM7.10 0.54 2.0 0.1  8 mM 12 mM  6.91 0.71 2.0 <0.1  4 mM 16 mM  6.76 0.942.0 0.1 20 mM  6.60 1.30 2.1 0.1 16 mM  4 mM 6.50 1.71 4.2 <0.1 12 mM  8mM 6.37 2.17 precip- nd itated 8 mM 12 mM  6.26 2.75 precip- nd itated 4mM 16 mM  6.15 3.38 precip- nd itated 20 mM  6.03 4.18 precip- nd itated

EXAMPLE 12

[0061] The profile of milk additions of magnesium and calcium withorthophosphates is shown in table 7 TABLE 7 Before heat Added AddedAdded Added Free After heat (90° C./10 min) MgCl₂ CaCl₂ K₃PO₄ K₂H PO₄ pHCalcium Viscosity¹ Sediment² 20 mM — — — 6.37 4.31 precipitated nd 20 mM0   12 mM 8 mM 7.10 0.52 2.05 0.1 16 mM  4 mM 12 mM 8 mM 7.05 0.65 2.050.2 12 mM  8 mM 14 mM 6 mM 7.09 0.66 2.1 <0.1  8 mM 12 mM 14 mM 6 mM7.06 0.76 2.16 <0.1  4 mM 16 mM 16 mM 4 mM 7.16 0.74 2.3 0.1  2 mM 18 mM16 mM 4 mM 7.13 0.83 2.34 0.3 0 20 mM 16 mM 4 mM 7.12 0.85 2.37 0.4

EXAMPLE 13

[0062] The relative performance of orthophosphates and other complexingagents on the distribution of calcium and protein in the serum phase ofskim milk or mineral adjusted skim milk was examined.

[0063] Skim milk and mineral adjusted skim milks (20 mM added calcium)were prepared and the milk serum fractions were obtained bycentrifugation (70,000×g 90 minutes). The calcium and proteinconcentrations of each of the milks and their serum fractions wereanalysed. The types of protein present in the serum fractions of theskim milk and mineral adjusted skim milk were determined by capillaryelectrophoresis. The results of experiments are shown in table 8.

[0064] Distribution of Calcium

[0065] The control (unadjusted) skim milk demonstrates that the calciumconcentration of the supernatant (serum) phase of the milk was of theorder of one quarter of the concentration in the un-fractionated milk.The addition of calcium alone to the milk, caused little change in theproportion of the calcium in the serum phase. The addition oforthophosphate (PO₄ ³⁻) in association with calcium caused aconsiderable reduction in the proportion of calcium in the serum phase.When longer chain forms of phosphate; pyrophosphate (P₂O₅),tripolyphosphate (P₃O₁₀) or Calgon T (P_(n)O_(3n+1) n==10˜12) were addedin combination with calcium chloride there was also a reduction in theproportion of the calcium in the serum phase but to a lesser extent thanthat occurring with orthophosphate. The addition of citrate caused amajor increase in the proportion of calcium in the serum fractionincreasing it to more than twice that seen in either unadjusted milk ormilk with 20 mM added calcium.

[0066] Distribution of Protein

[0067] The control (unadjusted) milk demonstrates that the normalprotein concentration of the milk serum was about one fifth of theprotein concentration of the unfractionated milk. The majority of theserum proteins are the “whey” proteins but a small proportion are serumcaseins which occur in equilibrium with the micellar caseins. Theaddition of calcium alone, or calcium and ortho-phosphate to the milkcaused a reduction in the relative concentration of protein in the milkserum, implying that the calcium, ortho-phosphate, and protein migratetogether into the micellar phase. Addition of pyro-phosphate has asimilar effect to the addition of ortho-phosphate, whiletripoly-phosphate and citrate cause an increase in the proportion ofprotein found in the serum. Calgon T has an effect intermediate betweenortho-phosphate and citrate.

[0068] Distribution of Protein Types

[0069] Analysis of the control (unadjusted) milk and the serum phases ofthe control and adjusted milks demonstrated little change in the levelsof the two major whey proteins β lactoglobulin and α-lactalbumin withany of the treatments. This indicates that these proteins, which formthe majority of the serum proteins, are not involved in the mineralinduced re-distribution between serum and micellar phases. Considerablechanges were observed in the distribution of caseins. In general thepatterns shown follow the changes observed in the analysis of proteinnitrogen. Adding calcium causes a reduction in the supernatant caseinconcentration compared to the supernatant from un-modified skim milk.This is also observed when orthophosphate or pyrophosphate are addedtogether with the calcium. The addition of tripolyphosphate, or citratewith calcium cause an increase in the levels of the caseins in the serumphase to varying degrees. Calgon T has an effect intermediate betweenortho-phosphate and citrate.

[0070] The patterns shown here demonstrate that there are clearlyidentifiable differences in the effect that a number of differentcalcium complexing agents have on the distributions of protein andcalcium between the serum and micellar phases of skim milk The preferredingredient for our process, orthophosphate can easily be differentiatedfrom other typically used agents such as citrate or poly phosphatethrough an evaluation of the protein contents of the supernatant phases.Citrate also causes a markedly different distribution of calcium. Of thetwo other forms of phosphate tested, tripolyphosphate shows considerabledifferences in the protein distribution, while although pyrophosphate isnot easily distinguished by these methods other tests have shown that itis less effective in providing stabilisation. TABLE 8 Levels of calciumand protein in complete and serum fractions of control milk (unadjusted)or mineral adjusted skim milks: Calcium Protein total super- relativetotal super- relative solution natant concen- solution natant concen-trial mg/litre mg/litre tration % % tration Control milk 1 1240 30724.8% 3.16 0.68 21.6% 2 1230 326 26.5% 3.11 0.66 21.2% Milk + 20 mMCaCl₂ 1 2085 496 23.8% 3.11 0.52 16.8% 2 2205 602 27.3% 3.55 0.57 16.0%Milk + 20 mM CaCl₂ + 1 2123 264 12.4% 3.22 0.57 17.8% 20 mMorthophosphate 2 2063 310 15.0% 3.11 0.53 17.1% Milk + 20 mM CaCl₂ + 12058 365 17.7% 3.09 0.58 18.8% 4 mM pyrophosphate 2 2068 484 23.4% 2.870.52 18.2% Milk + 20 mM CaCl₂ + 1 2068 352 17.0% 3.09 1.01 32.9% 8 mMtripolyphosphate 2 2088 389 18.6% 3.20 0.80 24.9% Milk + 20 mM CaCl₂ + 12223 367 16.5% 3.36 0.69 20.5% 0.15% Calgon T 2 2078 471 22.6% 3.19 0.5417.0% Milk + 20 mM CaCl₂ + 1 2098 1325 63.2% 3.16 0.82 25.9% 20 mMCitrate 2 2020 1151 57.0% 2.94 0.74 25.2%

[0071] Relative concentrations are calculated as 100× concentration insupernatant/concentration in total solution.

EXAMPLE 14 Use of Fortified Milk Powders and Milk Concentrates in PilotScale Production if Ice Cream

[0072] Ice creams were manufactured at a pilot scale to investigate thesuitability of using calcium fortified milk powder with 8 g addedcalcium/kg fortified solids or calcium fortified milk concentratesmanufactured as described in Example 9 as ingredients. Control icecreams were produced using a non-fortified milk powder or concentratemanufactured at the same time as a control. Milk solids wereincorporated into the formulation by either using skim milk powder orskim milk concentrates.

[0073] Formulation

[0074] The compositions of the ice cream pre-mixes used were:Milk-solids-not-fat 11.00%, Milk fat 11.00%, Sucrose 14.00%, Guar Gum0.1% Carboxymethyl cellulose (CMC) 0.1%, and Glycerol monostearate (GMS)0.2%, Vanilla flavour 0.35%. The remainder of the formulation comprisedof water

[0075] Production of Ice Cream

[0076] The ice cream mixes were prepared by combining the milkconcentrates (obtained either directly from the plant or byreconstituting milk powder) with a blend of sugar, Guar Gum, and CMC inwater then adding an emulsifier-cream mix of GMS in cream. The completemix was then homogenised (40° C., 2500 psi first stage 500 psi secondstage) and pasteurised (80° C., 30 seconds) using a tubular heatexchanger. The appropriate amount of vanilla flavouring was then added.This mix was then “aged” at 4° C. for 24 hours. The aged ice cream mixwas frozen using a GELMAK 160 continuous ice cream freezer. The machinewas operated to give a temperature at the outlet of −5° C. Followingfreezing samples were stored at −30° C. for hardening (24 hours) thentransferred to −20° C. for storage.

[0077] Analysis

[0078] Analysis of the Ice Cream Took Place Seven Days After Freezing.

[0079] Meltdown

[0080] Meltdown tests samples were performed on samples filled directlyfrom the ice-cream freezer into specially prepared two-piece cylindricalplastic moulds. The samples were hardened as described above thenequilibrated at −20° C. before testing. Samples were removed from themoulds and placed on a stainless-steel mesh screen (3 mm mesh) and themass of the melted portion passing through the screen was recorded at 15minute intervals for up to two hours. Ice creams made with either thefortified or non-fortified milk powders melted at about the same rateand melted completely within 105 minutes. Where concentrates were used,the melting rates were different with the calcium fortified ice creammelting within 75 minutes while the control ice cream was still meltingafter 2 hours.

[0081] Firmness

[0082] Firmness was measured using an Instron Universal Testing Machine(model 5564) equipped with a 500N load cell. The force required topenetrate the sample with a 5 mm cylindrical probe at a speed of 50mm/min to a depth of 50 mm was recorded. Where fortified ornon-fortified milk powders were used no significant differences could beidentified between the control and calcium fortified samples. Withconcentrates control (unfortified) ice cream was slightly firmer.

[0083] Sensory Testing

[0084] Informal sensory testing was conducted by giving coded samples toindividuals and eliciting spontaneous impressions. Little difference inflavour could be found between the two products.

[0085] This work demonstrates that the milk powders or concentrates withenhanced levels of calcium, produced by the process as claimed in claim1, may be used to produce calcium fortified ice-cream which hasgenerally similar physical characteristics to non-fortified ice cream.The fortified ice cream has minimal flavour differences compared to thenon-fortified ice-cream.

EXAMPLE 15 Use of Fortified Milk Powders (8 g Added Calcium/kg FortifiedSolids) in UHT Applications.

[0086] Milk based beverages were prepared using calcium fortified milkpowders with 8 g added calcium/kg fortified solids produced as describedin Example 9 as the source of milk solids. The pH of the samples wasfurther adjusted through the use of Sodium hydroxide. They wereprocessed in model UHT equipment giving a heat treatment of 140° C. forthree seconds. The viscosity of the samples was determined afterheating. This demonstrates the potential for these powders to beutilised in sweetened dairy based beverages, provided the appropriate pHis selected. TABLE 9 Properties of milk based beverages (8.5% milksolids non-fat, 3.5% milk fat, and 6% sugar) produced with calciumfortifed milk solids before and after UHT treatment. After UHT treatmentBefore (140° C./3 seconds) UHT treatment Viscosity Sediment Sample pH(cPoise)¹ (ml/50 ml) Calcium fortified 6.72 off scale >20 low heat milkwith fat and sugar Calcium fortified 7.07 30.7 (12 rpm) 4 low heat milkwith fat and sugar. pH adjusted to ˜7.0 Calcium fortified 7.24 16.3 2low heat milk with fat and sugar. pH adjusted to ˜7.2 Calcium fortified7.44 8.12 1.4 low heat milk with fat and sugar. pH adjusted to ˜7.4

[0087] Conclusions

[0088] The mechanism of action of orthophosphate in milk is unique. Thisis because of its effects on the dynamic equilibria between Ca,phosphate and the casein micelle. In milk, addition of orthophosphatesreduces Ca activity as well as impacts on the composition of the caseinmicelle. Whilst orthophosphate and other agents such as polyphosphateand citrate can be used to improve the heat stability of other proteinssuch as soy proteins that are sensitive to heat, the action in systemsother than milk is mainly due to the lowering of the Ca activity. Thisreduces the sensitivity of the proteins to heat aggregation. Heatstability of Ca fortified milk with up to 25 mM added Ca has beensuccessfully achieved with judicious addition of orthophosphate and pHcontrol A 1:1 molar ratio of added Ca:added orthophosphate has generallybeen used to achieve heat stability in Ca fortified milks. Lower ratiosmay be used but this decreased the range of pH over which the Cafortified milks are heat stable. By selecting suitable combinations ofadded orthophosphates, the viscosity of the heated solution should below, and preferably less than about 3 cPoise and the sediment obtainedon centrifugation of heated solutions should be <0.5 ml/50 mL milk.

1. A process for producing a calcium and/or nutritional mineralfortified milk, the process including the steps of: a) adding a solublecalcium and/or nutritional mineral compound to a milk, b) adding eitherbefore or after the calcium and/or nutritional mineral addition aneffective amount of a phosphate which enables calcium and/or nutritionalmineral to migrate into the protein micelles and maintains the pH sothat it lies within a range from 6.5 to 7.5
 2. A process as claimed inclaim 1 in which the phosphate is pyrophosphate and/or an orthophosphate consisting of one or more of monosodium dihydrogenorthophosphate, disodium hydrogen orthophosphate, trisodiumorthophosphate, monopotassium dihydrogen orthophosphate, dipotassiumhydrogen orthophosphate and tri potassium orthophosphate.
 3. A calciumand/or nutritional mineral fortified milk which includes milk, a calciumand/or nutitional mineral compound and an amount of a phosphate whichenables calcium and/or nutritional mineral to migrate into the proteinmicelles and maintains the pH so that it lies within a range from 6.5 to7.5, effective in stabilising the milk during heat treatment.
 4. Acalcium and/or nutritional mineral fortified milk as claimed in claim 3in which the phosphate is an orthophosphate consisting of one or more ofmonosodium dihydrogen orthophosphate, disodium hydrogen orthophosphate,trisodium orthophosphate, monopotassium dihydrogen orthophosphate,dipotassium hydrogen orthophosphate and tri potassium orthophosphate. 5.A process for producing a calcium and/or nutritional mineral fortifiedmilk or toned milk powder, the process including the steps of: a) addinga soluble calcium and/or nutritional mineral compound to a milk, b)adding either before or after the calcium and/or nutritional mineraladdition an effective amount of a phosphate which enables calcium and/ornutritional mineral to migrate into the protein micelles and maintainsthe pH so that it lies within a range from 6.5 to 7.5 c) pasteurising orheating the calcium and/or nutritional mineral fortified milk, and d)concentrating and dehydrating the milk to form a calcium and/ornutritional mineral fortified dry milk or toned milk powder.
 6. Afortified milk as claimed in claim 3 in which the nutritional mineral isselected from one or more water soluble compounds of magnesium, iron,zinc and manganese.